hgwebdir: avoid systematic full garbage collection
Forcing a systematic full garbage collection upon each request
can serioulsy harm performance. This is reported as
https://bz.mercurial-scm.org/show_bug.cgi?id=6075
With this change we're performing the full collection according
to a new setting, `experimental.web.full-garbage-collection-rate`.
The default value is 1, which doesn't change the behavior and will
allow us to test on real use cases. If the value is 0, no full garbage
collection occurs.
Regardless of the value of the setting, a partial garbage collection
still occurs upon each request (not attempting to collect objects from
the oldest generation). This should be enough to take care of
reference cycles that have been created by the last request
(assessment of this requires changing the setting, not to be 1).
In my experience chasing memory leaks in Mercurial servers,
the full collection never reclaimed any memory, but this is with
Python 3 and biased towards small repositories.
On the other hand, as explained in the Python developer docs [1],
frequent full collections are very harmful in terms of performance if
lots of objects survive the collection, and hence stay in the
oldest generation. Note that `gc.collect()` is indeed trying to
collect the oldest generation [2]. This happens usually in two cases:
- unwanted lingering objects (i.e., an actual memory leak that
the GC cannot do anything about). Sadly, we have lots of those
these days.
- desireable long-term objects, typically in caches (not inner caches
carried by repositories, which should be collected with them). This
is a subject of interest for the Heptapod project.
In short, the flat rate that this change still permits is
probably a bad idea in most cases, and the default value can
be tweaked later on (or even be set to 0) according to experiments
in the wild.
The test is inspired from test-hgwebdir-paths.py
[1] https://devguide.python.org/garbage_collector/#collecting-the-oldest-generation
[2] https://docs.python.org/3/library/gc.html#gc.collect
Differential Revision: https://phab.mercurial-scm.org/D11204
#require fuzzywuzzy
$ cat >> $HGRCPATH << EOF
> [extensions]
> releasenotes=
> EOF
Bullet point with a single item spanning a single line
$ hg debugparsereleasenotes - << EOF
> New Features
> ============
>
> * Bullet point item with a single line
> EOF
section: feature
bullet point:
paragraph: Bullet point item with a single line
Bullet point that spans multiple lines.
$ hg debugparsereleasenotes - << EOF
> New Features
> ============
>
> * Bullet point with a paragraph
> that spans multiple lines.
> EOF
section: feature
bullet point:
paragraph: Bullet point with a paragraph that spans multiple lines.
$ hg debugparsereleasenotes - << EOF
> New Features
> ============
>
> * Bullet point with a paragraph
> that spans multiple lines.
>
> And has an empty line between lines too.
> With a line cuddling that.
> EOF
section: feature
bullet point:
paragraph: Bullet point with a paragraph that spans multiple lines.
paragraph: And has an empty line between lines too. With a line cuddling that.
Multiple bullet points. With some entries being multiple lines.
$ hg debugparsereleasenotes - << EOF
> New Features
> ============
>
> * First bullet point. It has a single line.
>
> * Second bullet point.
> It consists of multiple lines.
>
> * Third bullet point. It has a single line.
> EOF
section: feature
bullet point:
paragraph: First bullet point. It has a single line.
bullet point:
paragraph: Second bullet point. It consists of multiple lines.
bullet point:
paragraph: Third bullet point. It has a single line.
Bullet point without newline between items
$ hg debugparsereleasenotes - << EOF
> New Features
> ============
>
> * First bullet point
> * Second bullet point
> And it has multiple lines
> * Third bullet point
> * Fourth bullet point
> EOF
section: feature
bullet point:
paragraph: First bullet point
bullet point:
paragraph: Second bullet point And it has multiple lines
bullet point:
paragraph: Third bullet point
bullet point:
paragraph: Fourth bullet point
Sub-section contents are read
$ hg debugparsereleasenotes - << EOF
> New Features
> ============
>
> First Feature
> -------------
>
> This is the first new feature that was implemented.
>
> And a second paragraph about it.
>
> Second Feature
> --------------
>
> This is the second new feature that was implemented.
>
> Paragraph two.
>
> Paragraph three.
> EOF
section: feature
subsection: First Feature
paragraph: This is the first new feature that was implemented.
paragraph: And a second paragraph about it.
subsection: Second Feature
paragraph: This is the second new feature that was implemented.
paragraph: Paragraph two.
paragraph: Paragraph three.
Multiple sections are read
$ hg debugparsereleasenotes - << EOF
> New Features
> ============
>
> * Feature 1
> * Feature 2
>
> Bug Fixes
> =========
>
> * Fix 1
> * Fix 2
> EOF
section: feature
bullet point:
paragraph: Feature 1
bullet point:
paragraph: Feature 2
section: fix
bullet point:
paragraph: Fix 1
bullet point:
paragraph: Fix 2
Mixed sub-sections and bullet list
$ hg debugparsereleasenotes - << EOF
> New Features
> ============
>
> Feature 1
> ---------
>
> Some words about the first feature.
>
> Feature 2
> ---------
>
> Some words about the second feature.
> That span multiple lines.
>
> Other Changes
> -------------
>
> * Bullet item 1
> * Bullet item 2
> EOF
section: feature
subsection: Feature 1
paragraph: Some words about the first feature.
subsection: Feature 2
paragraph: Some words about the second feature. That span multiple lines.
bullet point:
paragraph: Bullet item 1
bullet point:
paragraph: Bullet item 2
Warn user in case of unexpected block while parsing
$ hg init relnotes-warn
$ cd relnotes-warn
$ touch feature1
$ hg -q commit -A -l - << EOF
> commit 1
>
> .. feature::
>
> new feature added.
> some words about the feature.
> EOF
$ hg releasenote -r .
changeset a4251905c440: unexpected block in release notes directive feature
New Features
============
* new feature added. some words about the feature.
$ cd ..